Scientists rely on wet bulb temperature to assess the risk from heat, which is the point at which the human body cannot cool down. In many parts of the world, temperatures are never too hot for people to live in, especially in relatively dry climates. However, when it’s hot outside in dry places, most of the time the human body can cool down by evaporating water and heat from the skin through sweat.
But there are some places that are sometimes dangerously hot and humid, such as hot deserts next to warm oceans. When the air is humid, sweat doesn’t evaporate as quickly, so sweating doesn’t help cool the body like it does in drier environments. This combination can be particularly dangerous in some parts of Asia and Africa, where summer heat waves can combine with moist air blowing from the sea. Hundreds of millions of people live in those areas without air conditioning in their homes.
During a severe heat wave in 2023, wet bulb temperatures were very high in the Mississippi Valley, although not deadly. In Delhi, India, where air temperatures were higher than 49 degrees Celsius for several days in May 2024, wet bulb temperatures were near dangerous levels. Some people die from strokes in hot and humid weather. In such conditions, everyone must take precautions to prevent dehydration and stay safe from extreme heat and humidity.
Climate change also contributes to these risks by increasing global temperatures through emissions of carbon dioxide (CO2) into the atmosphere. The burning of fossil fuels like coal at power plants or gasoline in cars releases CO2 into the atmosphere trapping sunlight near Earth’s surface and leading to global warming. Each degree Celsius increase in temperature increases wildfires risk sixfold in western United States regions due to more moisture caused by evaporation of water bodies resulting from climate change impacts on agriculture practices causing irrigation water usage increase moisture content of air leading to wildfire outbreaks
